The BBC has released the trailer for the next Doctor Who special, "The Waters Of Mars," which showed at Comic Con yesterday. On second viewing, there's a lot more to this episode than just wet scabby death. Spoilers below.

Could we finally be about to get Russell T. Davies' theory of time travel? We've always had hints that there's a web of time, and certain events can't be changed or the whole universe comes apart. And maybe now we're about to get a bit more elaboration on that theme, which will make our nerdy little brains pulsate. For my money, the third best episode of Doctor Who season four was "The Fires Of Pompeii," and I'm hoping for a bit of a thematic sequel: Once again, the Doctor knows that history can't change, or it's all over. Of course, if his opposite number, the Master, turns up, he might just possibly have a slightly different agenda.

Rather than just being the throwaway adventure on our way to the final two-parter, it's beginning to seem like "Waters Of Mars" may be a corker in its own right. Here's hoping. Thanks to Jeremie for the heads up!